A chuck normally has a chuck body rotatable about an axis and carrying a plurality of angularly spaced jaws. A tightening body provided on the chuck body can be rotated relative to the chuck body to displace the jaws radially inwardly toward one another when the tightening body is rotated in a tightening direction about the axis of the chuck body, and to displace the jaws radially apart on rotation of the tightening body relative to the chuck in an opposite loosening direction. It is also known to provide mechanism in the chuck which converts forces exerted on the jaws during rotation in one direction into countervailing forces that tighten these jaws.
Nonetheless it is frequently necessary, as in a hammer drill, to provide further mechanism to prevent rotation of the tightening body in the loosening direction on the chuck body as a result of vibration during use. Thus my copending applications Ser. Nos. 011,722; 011,773; and 011,774 all filed Feb. 13, 1979 show various expedients used for relatively locking the tightening and chuck bodies against rotation of the tightening body on the chuck body in the loosening direction. Further such arrangements can be seen in German utility models Nos. 7,222,008 and 7,524,037, as well as in German patent publications Nos. 2,133,142, 2,341,642, and 2,639,214 and in U.S. Pat. No. 1,296,501.
The various nonloosening chucks have a locking element provided either on the tightening body or chuck body and engageable with teeth on the other body. Normally the locking body is carried on the chuck body and the teeth are formed on the tightening body, which itself is formed as a sleeve surrounding the chuck body. In order to ensure that the chuck body can only loosen at most a small amount, the teeth are made as fine as practical, and the locking element is provided with a small tip that can engage between the teeth. The fineness of the ratcheting or indexing can even be increased by providing several such locking elements which are spaced apart by angular distances not equal to whole-number multiples of the angular tooth spacing, so that the various locking elements will engage one after the other and will provide a number of locking positions equal to a multiple of the number of teeth.
The considerable disadvantage with this type of system is that the effort to make the indexing as fine as possible leaves the elements which hold the chuck and tightening bodies against relative rotation extremely small. Thus the teeth are very fine and the tooth or engaging part of the locking element is also extremely small. As a result the angular forces which these elements can resist are also correspondingly small. It is not uncommon for such a chuck to fail, normally by simply stripping of the teeth in the tightening sleeve or breaking-off of the tooth or teeth of the locking element.